Copy-paper



June 1957 R. OWEN 3,328,167

COPY-PAPER Filed Aug/10, 1959 I2 L i LIGHT-SENSITIVE LAYER H 4 VISIBLYHEAT-SENSITIVE LAYER 2 SUPPORT LIGHT-SENSlTlVE HEAT-STABILIZEDCOPY-PAPER IN V EN TOR.

RICHARD OWEN BY and, mm f ATTORNEYS 2 United States Patent 3,328,167COPY-PAPER Richard Owen, Brooklyn Center, Minn., assignor t0 MinnesotaMining and Manufacturing Company, St. Paul, Minn., a corporation ofDelaware Filed Aug. 10, 1959, Ser. No. 832,793 11 Claims. ((11. 96--67)This invention relates to the formation of permanent visiblereproductions of light-images, and has particular reference to sensitivesheet material or copy-paper adapted thereto.

In one aspect, the present invention makes possible the formation ofpermanent stable reproductions of lightimages while avoiding anynecessity for chemical stabilization or fixing, or other treatment withaqueous solutions, vapors, or other external chemical agencies. Theinvention also makes possible the intensificaton of indistinctly visiblereproductions of lightimages obtained by more conventional methods andwhich may involve initial chemical or other image-development. Thus, theinvention permits the effective utilization of light-sensitivemechanisms which of themselves do not directly provide visible copies,or copies of adequate intensity or of an effective degree of stability.The invention also provides means for directly producing visiblereproductions of low intensity light-images on heat-sensitivecopy-papers, and hence makes possible such procedures as the making offullscale or enlarged reproductions of original graphic subjectmatterfrom reduced photographic negative copies, or microfilm copies, of suchsubject-matter. The invention furthermore permits the copying of allvisible subjectmatter, including the making of portraits or the like aswell as the copying of colored ink drawings, signatures, paintings,etc., on heat-sensitive copy-paper.

The invention will now be described in terms of illustrative butnon-limitative specific embodiments.

Example 1 A transparent, visibly heat-sensitive copy-paper is firstprepared by coating a transparent polyester film backing (Mylar film)with a mixture of ferric stearate and t-butyl catechol in a solution ofethyl cellulose binder, and removing the solvent by evaporation at roomtemperature. The resulting sheet has a faint buff color, changingrapidly to blue-black when heated, eg. to about 100 C. It is suitablefor making reproductions of typewritten correspondence or other graphicoriginals by methods disclosed in Miller et al. US. Patents Nos.2,663,654-7, which also describes various additional typicalheatsensitive copy-sheet structures and formulations having utility inthe present invention.

Over the heat-sensitive layer is next applied a thin coating of asolution of equal parts by weight of silver nitrate andpolyvinylpyrrolidine binder in a solvent mixture of two parts of Waterand nine parts of methyl alcohol. The solution is preferably prepared,coated and dried under dark-room conditions or at least under subduedlight.

The resulting sheet is contact printed by exposure of the coated surfacefor six minutes to ultraviolet radiation from a EH-6 lamp at a distanceof six inches and through a photographic negative held in contact withthe sensitized surface. Close inspection of the thus exposed sheet showsa very faint brownish image corresponding to the transparent areas ofthe photographic negative.

The sheet is then briefly irradiated with high intensity light rich ininfra-red rays. Apparatus for carrying out this step of the process isdescribed in the Miller et al. patents hereinbefore referred to; and seealso Miller US. Patents Nos. 2,740,895-6. A dense blue-black image on abuff background is formed, corresponding to the initial faint brownishimage, and fully visible through the transparent film backing. The copyas thus viewed is stable on long aging even though the back surfacegradually darkens to a uniform gray-brown appearance or is otherwisealtered.

Example 2 A heat-sensitive copy-sheet consisting of a thinheattransparentizable opaque water-resistant coating of hydrogenatedfatty oil wax particles and cellulosic binder on a thin transparentpaper support previously coated with a thin layer of titanium dioxidepigment, an infra-redtransrnitting blue lake pigment, and polymericbinder, all as more fully described in Clark et al. US. Patent No.2,710,263, is supplied on the uncoated surface of the support with avery thin layer of silver halideagelatin photographic emulsion, appliedand dried under darkroom conditions. The sheet is briefly exposed to anenlarged light-image projected from a microfilm transparency, producinga latent image, and a corresponding visible image is developed bytreatment of the silver halide layer with a conventional photographicdeveloper solution. A faint black image is obtained, the darker areascorresponding to the light-Struck areas. The dried sheet is then exposedto brief intense irradiation as in Example 1, resulting in the selectivetransparentizing of those portions of the waxy coating overlying thedeveloped visible image. A high contrast reproduction of the originallight image is thus obtained, having deep blue image areas against awhite background as viewed from the wax-coated side. Further exposure tolight of the unstabilized silver halide layer causes a general darkeningof said layer, but without impairing the legibility of the image asviewed from the heatsensitive side. This darkening may be avoided byfixing and washing if desired.

The procedure just described permits the taking of photographs for thereproduction of printed or other graphic originals with minimum exposureto light, but requires the additional step of chemical development ofthe latent image. Similar sheets may be used in the procedure describedin connection with Example 1, but with increased exposure to directlyprovide a temporarily useful intermediate reproduction of the typeobtained with photographic print-out papers.

Example 3 A visibly heat-sensitive copy-paper of the type described inconnection with Example 1 is coated with a thin layer of an ironammonium citrate-potasssium ferricyanide solution as employed in makingblueprint paper. Mixing, coating, and drying are carried out underdarkroom conditions. Exposure of the dried treated surface to alightimage causes darkening of the surface in the light-struck areas.The resulting print may if desired be stabilized by washing with wateror preferably with a dilute solution of potassium dichrornate, anddried, and then irradiated with infra-red to develop a correspondingpermanent image in the visibly heat-sensitive layer. Alternativel theintermediate print may be irradiated without being stabilized, in whichcase the entire light-sensitive layer eventually darkens while theheat-sensitive layer retains the stabilized image.

Example 4 The light-sensitive blueprinting composition of Example 3 issimilarly applied to a transparent supporting web which carries on thereverse surface a heat-transparcntizahie opaque coating of a mixture offusible wax particles and non-fusing binder as described in connectionwith Example 2. The intermediate image produced on exposure of thelight-sensitive layer to a light-image is reproduced in theheat-sensitive layer, by exposure to radiation high in infra-red, in theform of transparent image areas in a white opaque background. The bluecolor of the intermediate image is visible through these transparentareas, producing a blue-and-white stable print.

Example 5 A transparent supporting web is provided on one major surfacewith an infrared-absorptive visibly heat-sensitive layer prepared byincorporating titanium dioxide pigment in a ferric stearate-gallicacid-ethyl cellulose heat-sensitive composition. A white or light buffopaque coating is thus obtained which is convertible to a denseblue-black by contact with a heated article or by momentary exposure toappropriate high intensity illumination. The supporting web is providedon the opposing major surface with a slightly acidic light-sensitivelayer containing a diazonium salt and a coupling agent, as used in thepreparation of diazotype printing plates and the like, producing a faintyellow color.

The diazo-coated surface is first exposed to a light-image by exposurethrough a photographic negative transparency, and is treated withammonia to develop an intense colored image on a white or slightlyyellowish background. The resulting print is also a negative; i.e. thesensitive layer develops the intense color only in those areas notexposed to light.

The sheet is then exposed from the same surface to high intensity flashirradiation such as is produced by a 500 watt-second discharge betweenterminal electrodes in a inch quartz tube filled with xenon underreduced pressure, the flash having a duration of about 1000 microsecondswith peak intensity at about 100 microseconds. Darkening of theheat-sensitive layer occurs in areas corresponding to the backgroundareas of the previous negative print, thus producing a positive printhaving blue-black image areas on a white or light buff background.

Any diazotype light-sensitive layer may be used which produces imageareas capable of absorbing the radiations applied. In the specificexample, the image areas are converted to an intense yellow. Thebackground areas remain a faint yellow or are bleached to an off-white.

The intensity of the flash irradiation is sufficient to cause blisteringor other degradation of a photographic transparency. The proceduredescribed permits the production of a positive print from a negativeoriginal on a heat-sensitive copy-paper without danger of damage to theoriginal through overheating during exposure.

Example 6 Thin transparent paper (map overlay tracing paper) is firstcoated with a smooth uniform layer of a fluid dispersion of 125 parts byweight of ferric stearate and 35 parts of alcohol-insoluble precipitateof hexamethylenetetramine and pyrogallic acid in a solution of 30 partsof polyvinyl butyral in sufiicient alcohol to provide a coatablemixture. The coating is dried at room temperature, leaving a resid ualdried layer of approximately 0.7 lb. per sq. yd. A second coating of asuspension of about 12 parts of zinc oxide pigment in a solution ofabout 7 parts of ethyl cellulose in acetone is next applied and dried,producing a thin visibly opaque coating. The sheet is stored for severalhours under dark conditions and is then coated over the zinc oxide layerwith a thin layer of silver nitrate solution, e.g. by lightly rubbingwith a cotton swab moistened with the solution, the operation beingperformed under subdued light. After drying, the coated sheet is firstexposed to a light-image, causing darkening of the light-strucksilvercoated areas. It is then momentarily intensely irradiated withinfra-red on the imaged surface, producing a corresponding but much moredistinct image in the heat-sensitive layer which is visible through thetransparent paper support layer. Further exposure to light causesuniform darkening of the silvered surface without affecting the visibleimage in the heat-sensitive layer.

4 Example 7 In this example the zinc oxide-ethyl cellulose layer ofExample 6 is applied directly to the thin paper backing. After asuitable aging period under dark conditions, silver nitrate solution isswabbed over the coating and the sheet is dried, again in absence oflight. The resulting sheet darkens on exposure to light. Prior to suchexposure it is provided on the uncoated surface with a thin layer of aheat-sensitive composition of equal molar proportions of silverbehenate, behenic acid, and protocatechuic acid, together with resinousbinder material. The sheet is first exposed on the first-coated side toa light-image, producing a visible but slight darkening at thelight-struck areas. It is then briefly exposed on the same surface tohigh intensity infra-red radiation. The darkened image areasdifferentially absorb the radiation and the resulting heat-patterncauses a corresponding visible change in the heat-sensitive layer.During irradiation, the heat-sensitive surface is pref erably insulatedfrom contact with heat-absorptive surfaces. Viewed from theheat-sensitive surface, the copy is a black-on-white mirror image of theoriginal white-onblack light-image.

Zinc oxide is a preferred example of a particulate lightsensitiveelectron donor material. Other examples include photochromic complexcompounds such as and photoluminescent pigment materials such assilver-activated zinc sulfide. Such materials are known to provide freeelectrons under the action of ultra-violet light or equivalent actinicradiation. Likewise, silver nitrate is a preferred example of electronacceptor material which undergoes a visible change in contact with thethus irradiated zinc oxide; gold chloride and chloroplatinic acid actsimilarly under the same conditions. The color change occurring in thesilver nitrate-Zinc oxide layer on exposure to a light-image issuflicient to provide a degree of contrast adequate for many purposes,but the image is not permanent under subsequent illumination. On theother hand, the image obtained in the heat-sensitive layer is stable tolight and provides an image of improved contrast.

Example 8 Thin transparent paper is first provided with a heatsensitivelayer as described in connection with Example 1, and is then furthercoated with a thin continuous layer of four parts of stronglyphotoconductive zinc oxide in one part of the resinous copolyrner ofequal parts of styrene and isobutylene. The volatile ketone vehicle isremoved and the sheet stored under dark conditions.

For use, the sheet is placed against a grounded flat metal surface withthe coated surface uppermost and is electrostatically charged from aconductor adjacent thereto at a potential of about 2,000 volts. Thesheet is then exposed to a light-image, permitting dissipation of theelectrostatic charge at the light-struck areas. The resulting imagepattern is made visible by development with colored electrostaticallycharged powder. The powder adheres to the charged areas but not to thedischarged areas, producing a copy of the original lightimage. Thecopy-sheet is then suitably isolated from heatconductive surfaces andthe imaged area is briefly intensely irradiated. The radiation ispreferentially absorbed at the powdered areas and the resultingheat-pattern produces a corresponding visible image pattern in theheatsensitive layer which is seen as a mirror image through thetransparent paper carrier web.

Where a fusible color powder is used in developing the electrostaticimage, or a fusible binder is used in the photosensitive layer, thepowder is found to be permanently bonded to the surface of the sheet.Such action is not required, however, the powder may as effectively becompletely removed, as by brushing, once the image has been madepermanent in the heat-sensitive layer.

Various other light-sensitive materials may be substituted for theexemplary materials hereinbefore suggested. They may, for example, 'beself-developing, as with the blueprint paper composition of Example 3 orthe silver nitrate of Example 1 or the zinc oxide-silver ni tratecombinations of Example 6 or 7; or they may require chemicaldevelopmentof a latent image as with the silver halide layer of Example 2 or thediazotype coating of Example 5; or physical development may beindicated, as in the case of Example 8. Various other heat-sensitivelayers may likewise replace the chemically reactive color-producinglayers of Examples 1, 3, or 5-8, or the physically transparentizablelayers of Examples 2 and 4. Furthermore the copy-forming heat-patternmay be produced in the light-image areas, or as Example 5, in theheat-sensitive layer itself. Various other combinations andmodifications will occur on consideration of the disclosures hereof. Inall cases, there is formed at the light-sensitive layer a pattern ofimage and background areas which differ in visible appearance and inability to absorb light, thus permitting the subsequent development of acorresponding heat-pattern by momentary intense irradiation, andresulting in the production of a corresponding visible print pattern inthe heat-sensitive layer. Although the radiation may be primarilyabsorbed and the heating effect produced either in the darkened areas ofthe light-sensitive layer or in the unmasked areas of the heat-sensitivelayer, it Will be seen that in all cases the visibly different image andbackground areas of the converted light-sensitive layer will besignificantly dissimilar in their ability to absorb the radiationemployed in producing the heat-pattern with which the final print isdeveloped.

A typical light-and-heat-sensitive copy-sheet as hereinabove describedis illustrated in the accompanying drawing, showing a copy-sheetcomprising a supporting Web 10, a visibly heat-sensitive coating 11, anda light-sensitive coating 12. Various combinations of these componentsare contemplated; thus the two sensitive coatings may be on oppositesides of an extremely thin support web, as indicated in Examples 2 and7, or preferably on the same side as in the remainin examples, and theircoating outermost. Where the heat-sensitive coating is between thelight-sensitive coating and the support, the latter will normally betransparent; this structure is generally preferred, since the printedheat-sensitive coating is thus protected by the transparent support, andthe latter, particularly where a thin paper is employed, provides aneffective marking surface which Will accept subsequent pencil or othermarkings. The support web may be omitted, its function then beingprovided by the filmforming binder components of either or both of thesensitive layers. On the other hand, additional layers, e. g.transparent protective surface coatings, may be added if desired. Insome instances such layers assist in providing intense print-images inthe heat sensitive layer by helping to prevent loss of heat from thecomposite sheet during irradiation of the intermediate image.Alternatively, separate temporary heat barriers may be provided for thispurpose where desired.

The imageintensifying action of the copy-sheets of this invention makespossible the effective use of ordinarily less desirable light-sensitivecompositions. Thus, lightsensitive coatings which by themselves yieldimages of low visible intensity, or which are unstable when exposed tolight or other conditions of use, or which require prolonged orcomplicated treatment to stabilize, may be employed in theseconstructions with formation of fully effective permanent reproductionsof light-images.

I claim:

1. A duplicating sheet comprising a support, a lightinsensitive visiblyheat-sensitive thermographic coating, and a visibly light-sensitivecoating including a Water-soluble salt, said light-sensitive coatingbeing capable of forming visibly distinct infrared-absorptive images inthe light-struck areas, said thermographic coating being capable ofundergoing permanent visible changeonly in said light-struck areas bythe heating effect obtained when the shget so imaged is briefly exposedto high intensity infrare 2. The duplicating sheet of claim 1 whereinthe watersoluble salt is a silver salt.

3. The duplicating sheet of claim 1 wherein the watersoluble salt is aferric salt.

4. The duplicating sheet of claim 2 wherein the lightscnsitive coatingincludes zinc oxide.

5. The duplicating sheet of claim 2 wherein the lightsensitive coatingincludes polyvinyl pyrrolidone.

6. A unitary copy-sheet adapted for making a permanent thermographicreproduction of a light-image, comprising a thin paper-like support, aheat-sensitive coating capable of remaining substantially unchanged inappearance on prolonged light-exposure and of undergoing permanentvisible change on being briefly heated to a conversion temperaturewithin the approximate range of 60 to C., and a light-sensitive coatingconsisting essentially of zinc oxide and water-soluble silver salt.

7. A unitary copy-sheet adapted for making a permanent record of alight-image directed thereon and com prising a thin flexible support webhaving distributed thereover a light-resistant visibly heat-sensitivefirst mixture of reactant components which mixture on being brieflyheated to a conversion temperature within the approximate range of 60 to150 C. undergoes an irreversible chemical reaction with formation of avisibly distinct reaction product and, coextensive therewith, alight-sensitive second mixture of reactant components different fromsaid first mixture and including a water-soluble ferric salt and aferricyanide, and which on exposure to light undergoes an irreversiblechemical reaction with formation of a visibly distinctinfra-red-absorptive reaction product.

8. A unitary copy-sheet adapted for making a permanent visible record ofa light image and comprising a transparent support member and,distributed over one major surface of said support, an obscuringtransparentizable layer of particulate material fusible to permitpermanent visibility of said support through said layer on being brieflyheated to fusion temperature, and, coextensively distributed over theopposite surface of said support, a light-sensitive mixture of reactantcomponents including a water-soluble ferric salt and a ferricyanide andwhich on exposure to light undergoes an irreversible chemical reactionwith formation of a visibly distinct infra-red absorptive product.

9. A duplicating sheet for making a permanent thermographic reproductionof a light-image by a process involving exposing the sheet to saidlight-image so as to form an infra-red-absorptive image in thelight-struck areas, and briefly exposing to intense infra-red radiationto cause heating at said image areas and formation of an intensifiedpermanent image, said sheet comprising a support, a heat-sensitivecoating capable of remaining substantially unchanged in appearance onprolonged light exposure and of undergoing permanent visible change onbeing briefly heated, and over said heat-sensitive coating alight-sensitive coating comprising a water-soluble silver salt and areactant therefor, said light-sensitive coating being of such characterthat, upon exposure to a light image and without photographicdevelopment, it will produce an infrared absorptive deposit in thelight-struck areas.

10. A duplicating sheet as described in claim 9 in which thewater-soluble silver salt consists essentially of silver nitrate.

11. The method of making a permanent stable reproduction of a graphicoriginal on a unitary copy-sheet hav ing a light-resistant visiblyheat-sensitive layer and a coextensive light-sensitive layer, saidlight-sensitive layer being increased in radiation-absorbency onexposure to light and including a water-soluble salt, said methodcomprising exposing said light-sensitive layer to a light-image of saidoriginal to produce a visibly distinct differentiallyradiation-absorptive pattern having increased radiation absorbency atthe light-struck areas, and briefly irradiating said pattern with highintensity radiation which is preferentially absorbable in said areas ofincreased radiation absorbency, whereby to cause localized heating and avisible change in the heat-sensitive layer at the location of the saidlight-struck areas.

References Cited UNITED STATES PATENTS 1,285,015 11/1918 Browning 96'681,303,635 5/1919 Capstaif 9668 1,880,449 10/1932 Hickman et al. 9612,036,369 4/1936 Simjian 9668 2,134,546 10/1938 Barth et al. 96692,159,600 5/1939 Murray et a1. 9669 2,316,803 4/1943 Michaelis 96-72,326,012 8/1943 Dalton 9688 8 Jelley et al. 9669 Anspon et al 9668Grandadarn 961 Clark et a1. 117-76 Kendall 9668 Moncriefl-Yeates 96-1Miller 11776 Owens 11734 Giairno 961 France.

Examiners.

R. BURROUGHS, W. C. GILLIS, J. T. BROWN,

Assistant Examiners.

1. A DUPLICATING SHEET COMPRISING A SUPPORT, A LIGHTINSENSITIVE VISIBLYHEAT-SENSITIVE THERMOGRAPHIC COATING, AND A VISIBLY LIGHT-SENSITIVECOATING INCLUDING A WATER-SOLUBLE SALT, SAID LIGHT-SENSITIVE COATINGBEING CAPABLE OF FORMING VISIBLY DISTINCT INFRA-RED-ABSORPTIVE IMAGES INTHE LIGHT-STRUCK AREAS, SAID THERMOGRAPHIC COATING BEING CAPABLE OFUNDERGOING PERMANENT VISIBLE CHANGE ONLY IN SAID LIGHT-STRUCK AREAS BYTHE HEATING EFFECT OBTAINED WHEN THE SHEET SO IMAGED IS BRIEFLY EXPOSEDTO HIGH INTENSITY INFRARED.